2 Answers
2

This is a change in sudo from lenny to squeeze. This change wasn't made to your sudoers file in order to preserve your customizations to /etc/sudoers.

Here's the entry from /usr/share/doc/sudo/NEWS.Debian.gz:

The sudo package is no longer configured using --with-secure-path.
Instead, the provided sudoers file now contains a line declaring
'Defaults secure_path=' with the same path content that was previously
hard-coded in the binary. A consequence of this change is that if you
do not have such a definition in sudoers, the PATH searched for commands
by sudo may be empty.
Using explicit paths for each command you want to run with sudo will work
well enough to allow the sudoers file to be updated with a suitable entry
if one is not already present and you choose to not accept the updated
version provided by the package.

I am not sure this is really his error, and may just have to do with the way he tried to figure out what his path was currently set too. I think he tried to run $PATH as a command to see the current path.
–
ZoredacheFeb 9 '12 at 0:26

Agreed. But I didn't want to leave that last question unanswered.
–
MeiFeb 9 '12 at 0:32

right, I just typed $PATH to get the PATH variable to see if it includes the path where adduser is located...
–
DominikFeb 9 '12 at 22:14